Tachycardia is a heart condition defined in an adult as a heart rate faster than 100 beats/minute. Tachycardia can broadly be classified as either sinus tachycardia, supraventricular tachycardia, or ventricular tachycardia. Sinus tachycardia is generally caused by exercise or emotional stress and is generally normal. Supraventricular tachycardia is defined as a tachycardia that originates above the bifurcation of the bundle of His. Ventricular tachycardia is defined as a tachycardia that originates below the bifurcation of the bundle of His. Some tachycardias are normal while others can have serious consequences including dramatically reducing cardiac output leading to chest pain, syncope, and death. As such, it is important to treat tachycardia appropriately.
Implantable medical devices are commonly used to treat patients with various conditions of the heart including tachycardias. In some cases, an implantable device is used to deliver a high-energy defibrillation or cardioversion shock to a patient's heart. Such shocks are generally successful at terminating tachycardias. However, defibrillation and cardioversion shocks cause extreme discomfort for patients.
Anti-tachycardia pacing (ATP) was developed as another implantable device-based technique for terminating tachyarrhythmias. ATP generally includes the delivery of a series of low-voltage pulses at a very rapid rate. These low-voltage pulses are generally delivered at the same voltage as regular pacing pulses used for treatment of bradycardia. Typically the initial interval between ATP pacing pulses is 80% of the R-R interval of the tachyarrhythmia to be treated. As such, the ATP pacing pulses are delivered at a rate that is faster than the tachyarrhythmia rate. ATP is effective in terminating some types of tachyarrhythmias. However, a need remains for additional techniques of terminating tachyarrhythmias.